Placing green twigs on the grave
What you have heard is correct. This Sahabi (companion of the Holy Prophet (Sallallahu alaihi wa sallam)) is Hadhrat Buraidah Aslami (May Allah Ta’ala be well pleased with him) who had willed that 2 green twigs be placed on his blessed grave. This Hadith is present in Sahih Bukhari, Vol. 1, Pg. No: 181.
Translation of Hadith: Hadhrat Buraidah Aslami (May Allah Ta’ala be well pleased with him) willed that 2 green twigs be placed on his grave.
Imam Bukhari (May Allah Ta’ala shower His mercy on him) has mentioned this Hadith in Kitab Ul Janaaiz and deduced the ruling on placing green twigs on the grave. Thus, he named this chapter "Babul Jareedi 'Alal Qabri" (placing (green) twigs on the grave)
It is well known among the Muhaddithin (the Hadith-experts) that the Ijtihad (deductions and/or opinion) of Imam Bukhari is expressed in the names of the chapters of Sahih Bukhari. The name of the chapter is his opinion and position on that issue and he makes deductions to prove/support the ruling on the particular issue.